The present invention relates to a suspension system adapted to be arranged between members located on the body side and wheel side of an automobile, and more specifically, to the improvement of a car suspension system having an oil chamber and a gas chamber incorporated therein.
Prior art suspension systems, which are adapted to contain oil and gas, comprise a cylinder housing and a rod fitted therein. An oil chamber and a gas chamber are defined inside the cylinder housing. Compressed gas, such as nitrogen, is sealed in the gas chamber. The expansion and compression of the gas inside the cylinder housing enables this system to act as a gas-spring mechanism. Damping-force generating means is provided inside the cylinder housing. The oil in the oil chamber is subjected to viscous resistance as it passes through the generating means, with the result that reciprocation of the rod is damped.
Conventionally known are suspension systems in which a sub-tank is located outside the cylinder housing. A shock absorber for automobile, as disclosed in U.S. Pat. No. 4,159,756, comprises a cylinder body and a tank, each having a gas chamber therein. The respective gas chambers of the cylinder body and the tank are connected to each other by a through hole. This shock absorber cannot, however, change its spring constant.
Meanwhile, a car suspension system as disclosed in U.S. Pat. No. 4,555,126 comprises a plurality of gas chambers and accumulators. These gas chambers and accumulators are connected by means of an air passage, e.g., an air pipe. The air passage is provided with a solenoid-control valve for opening and closing the passage. The spring constant of this suspension system is low when the valve opens. When the valve closes, the spring constant is high. In the suspension system constructed in this manner, however, the valve must have a high-accuracy seat and plug, in order to ensure that the air passage is tightly sealed when the valve is closed. This is because, unless the valve plug is in tight contact with the valve seat when the valve is closed, are will flow through the air passage. In such a case, the spring constant tends to become unchangeable.
Moreover, a shock absorber as disclosed in U.S. Pat. No. 4,527,676 comprises a tubular member having a plurality of orifices of different sizes, and an orifice adjuster having a cutout. The cutout is formed so as to communicate with an orifice of a desired size when the orifice adjuster is rotated by means of a motor. The damping force of the shock absorber varies in accordance with the size of the orifice. In this U.S. patent, however, there is no description of any gas spring mechanism. Therefore, this conventional shock absorber cannot change its spring constant.